Imagine one day you get a phone call from one of your customers. Great, a sale! Nope, just kidding! They are calling to tell you that your site has been hacked. What do you say? How did they find out before you did?
This is a scenario that every sysadmin dreads. How can you prevent something like this? A good defense in depth security strategy goes a long way in preventing this. This includes, WAF’s, firewalls, file integrity monitoring, IDS, two factor authentication, ASV scanning, event management, etc, etc.
The more layers you have, the better chance you have at either mitigating the attack, or being notified of the compromise shortly after it happens so you can react quickly and not have your clients inform you of the problem.
Below is another layer you can add: chkrootkit
Taken from the following wikipedia article (http://en.wikipedia.org/wiki/Chkrootkit):
chkrootkit (Check Rootkit) is a common Unix-based program intended to help system administrators check their system for known rootkits. It is a shell script using common UNIX/Linux tools like the strings and grep commands to search core system programs for signatures and for comparing a traversal of the /proc filesystem with the output of the ps (process status) command to look for discrepancies.
The document below will outline how to install and configure it for CentOS and Ubuntu, including how to run this nightly and email you the report for review.
Installing chkrootkit is pretty straight forward as shown below:
# CentOS 5 / RedHat 5 [root@web01 ~]# rpm -ivh http://dl.fedoraproject.org/pub/epel/5/x86_64/epel-release-5-4.noarch.rpm [root@web01 ~]# yum install chkrootkit mailx # CentOS 6 / RedHat 6 [root@web01 ~]# rpm -ivh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm [root@web01 ~]# yum install chkrootkit mailx # CentOS 7 / RedHat 7 [root@web01 ~]# rpm -ivh http://dl.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-5.noarch.rpm [root@web01 ~]# yum install chkrootkit mailx # Ubuntu / Debian [root@web01 ~]# apt-get update [root@web01 ~]# apt-get install chkrootkit mailutils
Perform a one time scan by running:
[root@web01 ~]# chkrootkit
Finally, lets setup a nightly cronjob and receive the report via email for review:
[root@web01 ~]# crontab -e 12 3 * * * /usr/sbin/chkrootkit | mail -s "chkrootkit Report : hostname.yourservername.com" [email protected]
Keep in mind that just setting up these tools doesn’t take care of the problem itself. The sysadmin needs to actively review any and all logs, software, etc. So with this tool and any security tool, identify false positives early on and exclude them from your reports so they are easier to read. This will help malware from slipping through the cracks of your logs and daily reports.
Several more articles will be following this in a series of sorts for malware detection. Each performs essentially the same function, but they go about it in different ways, each having their own benefits. Find the one(s) that work best for your solution.
Linux Malware Detect (maldet)